Design considerations for a radiation hardened nonvolatile memory

The authors discuss the design techniques used in the development of a 64 K EEPROM (electrically erasable programmable read-only memory) to maximize radiation hardness. Radiation testing has been performed on the 64 K EEPROM, demonstrating total dose hardness of greater than 1 Mrad (Si), immunity to data loss in a transient environment of greater than 1.4×10¹¹ rad(Si)/s, a write upset level of greater than 3×10⁹ rad(Si)/s, and a read upset level of greater than 1×10⁸ rad(Si)/s. The SEU (single event upset) soft error level ranged from an LET (linear energy transfer) of 35 to 50 MeV-cm²/mg for the various latches. Design modifications for reducing the standby current in a weapon environment and for increasing the transient upset level in the read mode are presented. The value of circuit simulations for predicting the radiation response of a nonvolatile memory and as well as for diagnosing radiation failures has been demonstrated